Turbine engines are widely used for a variety of purposes. For example, turbine engines are commonly used as propulsion engines in aircraft and other large vehicles. Turbine engines are also used in power generation. For example, turbine engines are commonly used as auxiliary power units in aircraft to supply electric power and compressed air. Large turbine engines are also used in power plants for electricity generation. In all applications the reliability and performance of the turbine engine is of critical importance.
One issue in turbine engine performance and reliability is the risk of combustion driven instabilities. In particular, oscillations of pressure in the turbine engine combustor can create control problems and possibly lead to turbine engine damage if allowed to continue. One cause of combustion driven instabilities is the natural resonance of the combustor. Natural pressure ripples in the combustor can feedback into the fuel system. This causes variations in the fuel flow to the combustor, which in turn causes the flame in the combustor to modulate, creating more pressure ripples. In some circumstances the natural resonant frequencies of the system will cause these pressure oscillations to constructively reinforce, leading to a potentially unacceptable level in pressure oscillations. This condition is commonly referred to as combustion instabilities or combustion dynamics. These types of combustion instabilities are particularly problematic in gaseous fuel turbine engines that are operated at high efficiency and low emission levels but can also exist in liquid fueled turbine engines.
Previous methods of compensating for these combustion instabilities have been limited. For example, some techniques have simply changed the power level of the turbine engine to move operation from frequencies that lead to instabilities. Unfortunately this is not an acceptable solution for applications where the power output of the turbine engine must be tightly controlled for efficiency or low emission purposes.